The present invention relates to an image forming system, image processing apparatus and image forming apparatus capable of adding an image for restraining copying to printed matter, and a memory product storing a computer program for realizing the image processing apparatus and the image forming apparatus.
As one of techniques for preventing copying of printed matter, a technique using a tint block pattern in the background of a document which is prohibited from being copied has been known. A tint block pattern consists of dots (foreground dots) in a size that remain even when a copy is made using a copying machine, and dots (background dots) which are so small and disappear when a copy is made. The background dots are arranged around the foreground dots so that characters and patterns drawn by the foreground dots are not noticeable. When printed matter on which a tint block pattern is formed is copied, the background dots disappear and only the foreground dots remain, and consequently the characters and patterns drawn by the foreground dots appear. Therefore, by embedding characters such as “copy-prohibited” and “confidential document” drawn by the foreground dots in the tint block pattern in advance, the printed matter to be produced can have the effect of restricting copying by itself.
The technique for preventing copying using a tint block pattern is mainly classified into two types. One is a technique using a special paper on which a tint block pattern is printed in advance, and the other is a technique in which a tint block pattern and a document are printed together as to be described later. With the former technique, by setting the special paper with the tint block pattern on a paper feed tray of a printer and printing a document, printed matter having the copy preventing effect is obtained. However, since it is necessary to prepare the paper on which the tint block pattern is printed in advance, such a technique has the problem of an increase in the cost of printing. Moreover, since predetermined characters and patterns for restricting copying are used, it is difficult to change the tint block pattern according to a document, and thus this technique also has the problem of lack of convenience.
Therefore, in recent years, a technique was proposed to print a tint block pattern on normal paper, etc. by providing a printer driver with the function of adding a tint block pattern to the image of a document to be printed (see, for example, Japanese Patent Application Laid Open No. H09-164739). According to this technique, in an information processing apparatus in which the printer driver is installed, the process of compositing image data for a document and image data for a tint block pattern is performed, and print processing is performed based on the image data obtained by compositing, and thus the document with the tint block pattern in the background can be formed on normal paper. Further, by preparing a plurality of types of tint block patterns in the printer driver, it is possible to select and use a tint block pattern according to a document.
However, the technique of adding a tint block pattern using a printer driver has a problem that this technique can be used only with a printer compatible with the printer driver, and its narrow application range has been pointed out. In other words, for printer drivers which have already been shipped in the market, it is necessary to wait for the function of printing a tint block pattern to be added by updates of the printer drivers or other method, and thus there is a problem, namely there is no guarantee that this function is available at the time the user wishes to introduce this technique. Besides, if a new printer having such a function is introduced instead of waiting for an update of the printer driver, it causes the problem of an extreme increase in the introduction cost.
Further, there is also a demand for copy protection for printed matter which is produced using a copying machine, but the demand has not been satisfied at present.